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Mosquitoes are major players world-wide as vectors for the causative agents of both human and animal diseases. Humans are the primary reservoir for Zika virus, Chikungunya virus and Dengue virus; however, we as veterinarians can be an important resource to educate the public on these emerging diseases.Aedes aegypti is the primary mosquito vector for these diseases. The importance of Aedes albopictus (the Asian tiger mosquito) is less clear, but this mosquito can transmit all of these viruses and is capable of surviving in more temperate climates.

THE MOSQUITOES

Aedes aegypti: This mosquito is originally from Africa and now has a global distribution through human trade and movement. Aedes aegypti enjoys cohabitation with people and is a very effective vector for the agents of [or viruses that cause] all three of these emerging diseases.

Aedes albopictus: The Asian tiger mosquito is believed to have arrived in the U. S. in a shipment of used tires from Asia. This mosquito now has a broader host range than Aedes aegypti since it can survive cooler temperatures.

Both of these mosquito species are container breeders and they can reproduce in very small amounts of standing water. This is why control efforts for them consist of proper management of water holding containers by cleaning up clutter and covering, dumping, modifying or treating water-holding containers with long-lasting larvicides. Both of these mosquito species are aggressive biters during the day as well as early morning and late afternoon.

THE DISEASES

Zika virus

This Flavivirus first was isolated in the Zika forest of Uganda in 1947.

In nature, Zika virus transmission likely is maintained in a monkey-mosquito-monkey cycle.

At this time there is no evidence of companion animals becoming infected with the virus.

A small number of cases of Zika possibly have occurred from sexual contact and since many cases are asymptomatic, transmission by blood transfusion could occur in high-risk areas.

People often have no symptoms when infected and if symptoms occur they rarely are sick enough to go to seek medical care and there are few deaths.

Symptoms other than fever consist of rash, joint pain and conjunctivitis and last for up to a week.

Zika virus has been associated with an increase in cases of microcephaly in infants and possibly Guillain-Barre syndrome in adults in Brazil.

Cases of Zika have occurred in the United States; however, sustained transmission is unlikely because of our increased surveillance, the use of screens to keep mosquitoes out of houses and the widespread use of air conditioning during the summer.

There is no vaccine for Zika virus so prevention of mosquito bites is important in regions where the virus is circulating. Infection with the virus likely gives long- term immunity to subsequent infections.

Women who are pregnant (any trimester) are advised by the CDC to not travel to any area where Zika virus transmission is ongoing.

Chikungunya virus

Chikungunya virus disease was first reported in 1952 in what is now Tanzania. The name is derived from an African verb that means “to dry up or become contorted”, a description of the posture of people with severe arthritis from the disease.

In Africa, Chikungunya virus circulates in nature among non-human primates and small mammals and their mosquitoes. Large human outbreaks can occur where wild animals are not needed for transmission.

A majority of people infected with Chikungunya virus become symptomatic and clinical disease primarily consists of a rapid onset of fever and poly arthralgia.

Symmetric joint symptoms often occur in the hands and feet, can be debilitating and relapses can occur. Some patients can experience joint pain for months or even years.

Other symptoms of the disease include headache, myalgia, arthritis, conjunctivitis, nausea, vomiting and a maculopapular rash.

Some cases of Chikungunya may be difficult to distinguish from Dengue clinically. This is important because the use of aspirin or nonsteroidal anti-inflammatory drugs (NSAIDS) can be used to treat pain in Chikungunya, but are contra-indicated in Dengue because they increase the risk from hemorrhage.

Severe disease is more likely to occur in neonates exposed intrapartum, adults older than 65 years and persons with other medical conditions such as hypertension, diabetes or cardiovascular disease.

Chikungunya virus is not known to infect domestic animals or companion animals.

Since there is no vaccine, prevention of mosquito bites is critical in areas where the virus is circulating.

Dengue virus

Early epidemics of Dengue were reported from Asia in the 18th century.

The name of this virus also is thought to be derived from an African phrase meaning “cramp-like seizure caused by an evil spirit”. Another possible derivation is from the Spanish word “dengue” which means careful. The early names for the disease describe the symptoms caused by pain in people who are infected.

There are four strains of the virus and initial infection with one strain generally results in a milder illness consisting of high fever severe headache, severe pain behind the eyes, joint pain, muscle and bone pain, rash and mild bleeding.

Infection with one strain of the virus provides protection against a second infection with that strain; however, infection with a different strain can result in dengue hemorrhagic fever.

Dengue hemorrhagic fever is believed to be an immune-mediated disease that initially presents with fever that declines followed by generalized capillary bleeding, abdominal pain, persistent vomiting and difficulty breathing. Without timely treatment, there is a high risk from death in hemorrhagic fever cases.

Treatment for dengue consists of supportive care and use of acetaminophen or paracetamol for fever and pain. NSAIDS and aspirin are contraindicated because of the risk of hemorrhage.

Dengue does not infect domestic or companion animals.

A phase 3 clinical trial presently is being conducted on a vaccine for Dengue.

Dengue

Alabama Department of Public Health Mosquito-borne Diseases site

OTHER DISEASES

Other mosquito species are involved; however, Aedes albopictus may be involved in transmission of Eastern equine encephalitis, Western equine encephalitis, West Nile virus and Dirofilaria immitis. The presence of this mosquito can likely increase the risk of human infection with these zoonoses.